如何从drupal 7以纯文本形式返回请求的响应？

I have drupal 7 configured on my system. By default it returns response in json format.

if ($op == 'condition1') {
    $output = 'output1';
    return $output;     
}
if ($op == 'condition2') { 
    $output = 'output2';  
    return (object)$output;
}

currently ,

condition 1 gives response as

[
"output1"
];

condtion 2 gives response as

[
"scaler" : "output2";
]

But I need response a simply as plain text eg output

I dont know what settings to change.

The available response formatters are bencode, json, jsonp, php, xml.

Thanks.